Initializing SSH Keys
The Public and Private keys are created on the client using ssh-keygen
The Private Key is stored securely on the client, and the Public Key is copied onto the server using ssh-copy-id
Logging in with SSH Key
When accessing the server via SSH, the server will send an encrypted packet to the client containing the Public Key, in which the client responds with the contents of the Private Key
Setting up SSH Key-based Login
ssh-keygen: Creates a public/private key pair for the current user
Setting a passphrase for the private key makes it more secure but also makes it less convenient to access the server
ssh-copy-id: Copies the public key to the target server
ssh-agent /bin/bash: If the private key has a set passphrase, this command allocates space in the bash shell to cache the passphrase
If this is done, ssh-add must be used to set the passphrase
Changing Common SSH Server Options
Server options are set in /etc/ssh/sshd_config
Port: Sets the port SSH listens on
PermitRootLogin: Enables/Disables root login
PubkeyAuthentication: Enables/Disables logging in via ssh-keys
PasswordAuthentication: Enables/Disables logging in with a password
X11Forwarding: Allows users to forward a graphical screen
AllowUsers: Specifies specific users that can access the system
The sshd daemon must be restarted if changes are made to /etc/ssh/sshd_config:
systemctl restart sshd
Securely Copying Files
scp: Used to securely copy files over the network using the sshd daemon
Syntax: scp [file1] [file2] [user]@[server]:[/path/]
sftp: Offers an FTP client interface to securely transfer files using SSH
put /file: Uploads a file
get /file: Downloads a file to the current working directory
Securely Synchronizing Files
rsync: Used to synchronize files via SSH
If the source and target file already exist, rsync will only synchronize their differences
Options
r: Recursive synchronization
l: Synchronizes symbolic links
p: Preserves symbolic links
n: Dry run
a: Archive mode, which is equivalent to -rlptgoD
A: Uses archive mode and also synchronizes ACLs
-X: Synchronizes SELinux context